This invention relates to a control apparatus, and more particularly to a piston type control apparatus whose piston operation is controlled by fluid means and/or mechanical means.
As an apparatus for controlling the pressure and/or flow quantity of a fluid flowing through a pipe-line a multivalve type control apparatus is well known which is so designed as to properly open and close valves disposed respectively in the pipes of a manifold system thereby to change over the flow course of a fluid flowing through these pipes thus to obtain a predetermined pressure and/or flow quantity of the fluid. In such control apparatus, however, when the valve opening and closing operation is performed, the pressure and/or flow quantity fail to obtain a stationary flow. Therefore, where this control apparatus is used in an oil pressure pipe-line for, for example, the injection ram of an injection machine, the unfree surface of a molded article becomes rough, or the free surface thereof becomes wavy. In addition, such control apparatus requires provision therein of many valves. As a result, the apparatus is made large in size and complicated in construction and high in cost. In addition, such control apparatus requires changeover of valves thus making its operation inconvenient. In addition, such control apparatus only enables the fluid to be set at a specific pressure and/or flow quantity, so that it is impossible to control the fluid non-stepwise.
Under these circumstances, as an apparatus for multistepwise controlling the fluid using a single valve a piston type control apparatus has been proposed which is so designed as to control the operation of a piston included therein using electromagnetic means. In such electromagnetic control apparatus, current is passed through a solenoid to excite the magnetic core, and its attractive force is designed to control the piston position. This control apparatus makes a continuous non-stepwise remote operation possible, but fails to completely prevent occurrence of the pulsation constituting a drawback inherent to an electromagnetic device, so that a stationary flow is not obtained. In addition, such control apparatus requires provision therefor of constant voltage means in particular, and as a result is made expensive and complicated in construction. In addition, such control apparatus has also the drawback that it is difficult to control the speed of the piston movement.